Envelope flap moistening systems generally fall into two categories, contact and non-contact moistening systems. Contact systems generally deposit moisture onto an envelope flap by contact with a wetted substrate. Non-contact systems generally spray moisture onto the envelope flap. In non-contact flap moistening systems, envelope flap moistening has been performed with nozzle and pump systems. The pump which is connected to a reservoir is also connected to spray nozzles. A solenoid actuated valve can be placed between the pump and the nozzle(s) to control spraying.
Some non-contact systems with pump(s) and nozzles rely on leading edge sensors and a time lag for compensating for the distance between the nozzle and the leading edge sensor for spraying fluid onto the glue area of the envelope flap. This method can be imprecise, spraying fluid onto an incorrect place on the envelope. Also, since the systems have few nozzles, they are not highly accurate. Other sensing systems, such as systems comprising an envelope sensor and a flap sensor, are designed to sense limited flap profiles, such as, profiles of no. 10 envelope flaps.
Other non-contact systems can have several nozzles. The nozzles which are not highly accurate produce considerable over-spray which can wet portions of the envelope flap which do not have a glue area and can also wet the contents of the envelope. The inaccuracy of some non-contact systems may also cause over spraying and/or miss portions of the flap, thus requiring a fluid collection means for collecting unused fluid. The size of the nozzles prohibits a larger number of nozzles to be placed in a small area of a mailing machine which is in alignment with an envelope flap path. Thus, an array of nozzles can be large and difficult to implement into a mailing machine. An example of a non-contact system is a pump and nozzle system. The amount of fluid that pump and nozzle systems use is large since the nozzles spray in a continuous manner, are imprecise and also over-spray.
Pump and nozzle systems can also require a large amount of space in the systems in which they are mounted. These pump systems usually include a pump and motor, and as such, they can be large and difficult to locate in the space available. Pumps, such as piston driven pumps, are difficult to control. Due to the response time of the system, the piston must start prior to the time the spray is desired, and must stop earlier than desired because the spray will continue after the piston stops due to inertia and system elasticity. In multiple nozzles systems, typically one pump supplies fluid to the nozzles and all of the nozzles are "on" or "off" simultaneously. The response time for spraying in a system that uses a pressurized fluid supply, a solenoid control valve, and spray nozzles is limited by the system's ability to pump fluid to the required place at the required time. The systems are dependent upon solenoid actuated valves which have a physical upper frequency limit of 200 to 500 Hz. The nozzles supply moisture in a continuous spray; therefore, controlling the amount of fluid applied to an envelope flap is not precise.
Thus, one of the problems of the prior art is that the nozzle and pump systems do not provide accurately metered amounts of fluid; therefore, over-wetting and under-wetting of the envelopes moistened by these systems results in poor, delayed or no sealing. Another problem of the prior art is that nozzle and pump flap moistening systems, which generally have one to three nozzles are only as precise as the number of nozzles allow. Another problem of the prior art is that nozzle and pump systems use more fluid than is necessary to moisten the glue area of an envelope flap. Another problem of the prior art is that response speed of nozzle and pump systems is limited. Another problem of the prior art is that limited flap profiles can be sensed by any one system, or multiple sensor systems are needed to sense numerous flap profiles. Another problem of the prior art is that continuous spray nozzles provide for poor moisture control. Another problem of the prior art is that over-spray requires fluid collection systems and causes wetting of envelope contents.